In recent years, LCD devices have become widely used in fields such as mobile phones, vehicular displays, PDAs (Personal Digital Assistant) and TVs. A typical LCD device includes an LCD panel and a backlight module mounted under the LCD panel for supplying light beams thereto. Therefore, the performance of the backlight module is an important factor of the display quality of an LCD device. Important characteristics of the backlight module include its high brightness, low cost, low power consumption, and thin and light design. High brightness and uniform illumination help an LCD provide good display performance.
FIG. 6 represents a typical backlight module 10 comprises a light guide plate (LGP) 12, a light source 14, a quarter wave plate 13, an upward prism plate 16 and a downward prism plate 18. The quarter wave plate 13, the LGP 12, the upward prism plate 16, the downward prism plate 18 are stacked continuously in that order from bottom to top. The LGP 12 defines a light incident surface 121, a light emitting surface 122 adjoining the light incident surface 121, and a bottom surface 123 opposite to the light emitting surface 122. The light source 14 is placed next to the light incident surface 121. The quarter wave plate 13 comprises a reflective film (not shown) on a backing surface 132 thereof.
The upward prism plate 16 includes a plurality of uniform upward micro-prisms 162 on a surface thereof opposite from the LGP 12, the downward prism plate 18 comprises a plurality of downward micro-prisms 182, and the micro-prisms 182 substantially mesh with the upward micro-prisms 162, but leaving a gap 19 therebetween.
Due to the foresaid structure of the backlight module 10, the p-polarized light of light coming from the LGP 12 can pass through the downward micro-prisms 182, while the s-polarized light thereof is reflected and converted into p-polarized light via the quarter wave plate 13 and then pass through the downward micro-prisms 182.
However, when defining the gap 19 between opposite surfaces 163 and 183 of the upward micro-prisms 162 and the downward micro-prisms 182, a locating mechanism is required for locating the downward prism plate 18. The structure of the backlight module 10 is thereby complicated, more time and high locating precision are required for the assembly. Furthermore, a difference of the each of the refractive indices of the prism plates 16, 18 and the gap 19 is in the range from 0.001 to 0.2. It's difficult to select suitable materials for the prism plates 16, 18.
What is needed, therefore, is a polarizer which has simple structure, can be assembled readily.
What is also needed, therefore, is a method for manufacturing the above-described polarizer.
What is also needed, therefore, is a backlight module using the above-described polarizer.